[Selective Adsorption of Au(â ¢) by Activated Carbon Supported Polythioamides and Adsorption Mechanism].

By using in-situ synthesis of polythioamide (PTA) on activated carbon (AC), a polythioamide-modified activated carbon-based adsorbent (AC-PTA) was successfully prepared and used to study the selective adsorption effect and mechanism of Au(Ⅲ) in wastewater. The results showed that AC-PTA exhibited excellent selective adsorption to Au(Ⅲ) in the coexisting solution of multiple metal ions in a wide pH range (<5.0). The adsorption effect for Au(Ⅲ) was the best at a pH of 2 and 3; the concentration of residue Au(Ⅲ) was less than 0.1 mg·L-1, whereas other metals were barely adsorbed. The selective adsorption process for Au(Ⅲ) conformed to the pseudo-second kinetic model (R2=0.9853), the thermodynamic process conformed to the Langmuir isotherm process (R2=0.9936), and adsorption capacity was up to 2018 mg·g-1. Such advantages were mainly attributed to the coordination interaction between the -C([FY=,1]S)NH- functional groups on the AC-PTA surface and Au(Ⅲ), the electrostatic adsorption between the positive AC-PTA and negative Au(Ⅲ) complex anions, and the direct reduction of Au(Ⅲ) by AC. The successful recovery of gold was finally realized by burning the adsorbed AC-PTA at 1000℃ for 4 hours under air conditions, and solid gold with a mass fraction higher than 90.0% was obtained. This study provided the possibility for selective adsorption and recovery of low concentration Au(Ⅲ) from actual wastewater.

[Application of Fenton-like Photocatalysts Based on Defect Reconstruction in Degradation of Dye Wastewater].

In recent years, improving the performance of catalysts through defect modulation has attracted extensive attention. However, the impact of defect rearrangement on Fenton-like photocatalytic reactions has not been studied. In this study, Fe-containing polyoxometalate molecules were grafted onto the surface of defective TiO2.The influence of oxygen vacancy formation and the defect arrangement process on the catalytic activity was investigated. The results indicated that the calcination of cyanamide modified defective TiO2 is beneficial for the spatial reconstruction of oxygen vacancies generated by H2 atmosphere treatment. With rearranged structural defects, photo-generated electrons were prone to transfer from the surface of P25 to Fe-POM nanoparticles. Due to the enhanced charge separation in TiO2 and the increased reactive sites on the Fenton-like reagent, Fenton-like photocatalysts with rearranged defects showed a 13-fold increase in catalytic activity during the degradation of dye molecules.

[Preparation of BiOCl-(NH4)3PW12O40 Photocatalyst and a Mechanism for Photocatalytic Degradation of Organic Pollutants].

The separation efficiency of photogenerated electrons and holes is the key to photocatalytic performance. Layered BiOCl is a kind of newly exploited efficient photocatalyst, but its wide-spread practical application is hindered by the rapid recombination of photogenerated electron-hole pairs and low quantum efficiency. In this study, we prepared a composite photocatalyst via a hydrothermal method in which (NH4)3PW12O40 (NH4PTA) is the acceptor of photoelectrons from BiOCl. The photocatalytic performance of variants of BiOCl-NH4PTA was evaluated by the removal efficiency of methyl orange (MO). The experimental results showed that the BiOCl-NH4PTA[n (Bi):n (W)=1:1] had the best photocatalytic activity under the irradiation of sunlight simulated by xenon light. The photocatalytic mechanism was investigated using the reactive species trapping experiments. It was found that MO could be photodegraded by,·OH, and holes over BiOCl. Differently, and·OH were the dominant reactive species for the reactions over the composite photocatalyst. It was proved that NH4PTA was the acceptor of photoelectrons by the XPS on the photocatalyst before and after reaction. The photocurrent test verified the superior photocatalysis of BiOCl-NH4PTA which was attributed to the efficient separation of electron-hole pairs.

[Preparation of ZnTiO3/TiO2 Photocatalyst and Its Mechanism on Photocatalytic Degradation of Organic Pollutants].

TiO2 is a promising photocatalysis for degradation of organic pollutants due to its innocuity. However, its widespread practical application was hindered by the fast combination speed of photogenerated electron-hole pairs and low quantum efficiency. In this study, we prepared ZnTiO3-TiO2 using the Sol-Gel method to get heterojunctions, which exhibit efficient separation of photogenerated electron-hole pairs. The photocatalytic performances of various ZnTiO3-TiO2 were evaluated by the removal efficiency of Methyl orange. The experimental results showed that the ZnTiO3-TiO2(ZnTiO3:TiO2=0.3), which was calcinated under 600℃, had the best photocatalytic activity under ultraviolet light. The photocatalyst was stable under a wide range of pH (2.5-12.5). The photocurrent and ESR analysis verified the superior photocatalysis of ZnTiO3-TiO2, which was attributed to the efficient separation of electron-hole pairs induced by the heterojunctions.

[Simultaneous Photocatalytic Reduction of Cr(â ¥) and Oxidation of SSA by Carbon Nitride].

Carbon nitride is a novel nonmetal semiconductor photocatalyst, which has developed into an ideal environmental treatment material in recent years. Graphite carbon nitride(g-C3N4) was prepared through pyrolysis melamine, and the structure, morphology and optical properties of samples were characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM) and UV-Vis diffuse reflectance spectra(UV-Vis DRS). The potential application of g-C3N4 in the simultaneous photocatalysis reduction of Cr(Ⅵ) and oxidation of sulfosalicylic acid(SSA) was further explored. And the effects of different conditions such as catalyst dosage, pH and initial concentration ratio of Cr(Ⅵ) with SSA on the simultaneous photocatalysis were also investigated. The results showed that when the catalyst dosage was 0.5 g·L-1, pH=2, the initial concentration ratio of Cr (VI) and SSA was 1:4(10 mg·L-1:40 mg·L-1), optimal simultaneous photocatalysis efficiency was achieved, which was more than 3 times higher than that of the separated photoreduction or photooxidation reactions. Within 3 hours, the reduction ratio of Cr(Ⅵ) and oxidation ratio of SSA could reach 98.9% and 93.4%, respectively. The mechanism of simultaneous photocatalysis was discussed. Cr(Ⅵ) was reduced by electrons and SSA was oxidized by the combined function of hole, O2·- and·OH under visible light.

Enhanced arsenic removal by in situ formed Fe-Mn binary oxide in the aeration-direct filtration process.

Field studies were conducted to evaluate the feasibility of an in situ formed Fe-Mn binary oxide (in situ FMBO) for improving arsenic (As) removal in the aeration-direct filtration process. The transformation and transportation of As, Fe, and Mn in the filter bed were also investigated. The in situ FMBO increased the As removal efficiency by 20-50% to keep the residual As below 10 µg/L. The optimum FMBO dosage was determined to be 0.55 mg/L with the Fe/Mn ratio as 10:1. The removal of Fe, Mn, turbidity, and particles was also improved to a large extent. The in situ FMBO favored the transformation of soluble As, Fe, and Mn into the solid phases, benefiting the removal of these pollutants by the subsequent filtration. Moreover, the deposited precipitates onto the filter media were characterized, as indicated by the analyses of SEM/EDS and particle size distribution. The long-term experiments exhibited decreased head loss growth and prolonged run length, suggesting an enhanced pollutant catching capacity of the filter media. The full-scale field study with a flow of 10,000 m3/d confirmed positive effects of in situ FMBO on As removal, with the average effluent As concentration reduced from 20 µg/L to 6 µg/L (reagent cost=0.006 ¥/m3).